Door viewer devices are security devices that permit a viewer located on one side of the door (e.g., the inside of the door) to observe callers located on the other side of the door (e.g., the outside of the door). Such door viewer devices typically include a lens system that generates a virtual image of the various objects located in front of the door. In operation, a user positioned behind the door peers through the door viewer device to view the immediate area surrounding the door, thereby enabling the person to confirm the identity of persons or objects before opening the door. Conventional door viewer devices suffer from several disadvantages. First, conventional door viewer devices permit two-way viewing. That is, while door viewer devices permit the viewer on the inside to view the area located in front of the door, they further permit a viewer positioned in front of the door to view the area proximate the rear side of the door. In addition, conventional door viewer devices permit outside viewers (i.e., persons located in front of the door) to view changes in light that occur when the insider viewer approaches the door and looks through the peephole. By noting changes in light within the peephole (e.g., from light to dark), the outside viewer is alerted to the fact that someone is located within the structure (e.g., the home, apartment, business, etc.) and is positioned behind the door, which compromises the security of the persons located within the structure.
Thus, it would be desirable to provide a security device that prevents outside viewers from viewing into the secured area (e.g., a house, office, etc.), as well as enables an insider viewer to look through the door viewer device without generating changes in light that might occur during viewing.